Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, data and so on. These systems may be multiple-access systems capable of supporting simultaneous communication of multiple terminals with one or more base stations.
A problem that must be dealt with in all communication systems is fading or other interference. There may be problems with decoding the signals received. One way to deal with these problems is by utilizing beamforming. With beamforming, instead of using each transmit antenna to transmit a spatial stream, the transmit antennas each transmit a linear combination of the spatial streams, with the combination being chosen so as to optimize the response at the receiver.
Smart antennas are arrays of antenna elements, each of which receive a signal to be transmitted with a predetermined phase offset and relative gain. The net effect of the array is to direct a (transmit or receive) beam in a predetermined direction. The beam is steered by controlling the phase and gain relationships of the signals that excite the elements of the array. Thus, smart antennas direct a beam to each individual mobile unit (or multiple mobile units) as opposed to radiating energy to all mobile units within a predetermined coverage area (e.g., 120°) as conventional antennas typically do. Smart antennas increase system capacity by decreasing the width of the beam directed at each mobile unit and thereby decreasing interference between mobile units. Such reductions in interference result in increases in signal-to-interference and signal-to-noise ratios that improve performance and/or capacity. In power controlled systems, directing narrow beam signals at each mobile unit also results in a reduction in the transmit power required to provide a given level of performance.
Wireless communication systems may use beamforming to provide system-wide gains. In beamforming, multiple antennas on the transmitter may steer the direction of transmissions toward multiple antennas on the receiver. Beamforming may reduce the signal-to-noise ratio (SNR). Beamforming may also decrease the amount of interference received by terminals in neighboring cells. Benefits may be realized by providing improved beamforming techniques.